Fibroblast Growth Factors (FGFs) promote growth, proliferation, survival and differentiation of a wide variety of cells and tissue types. The prototypic fibroblast growth factors (FGFs), FGF-1 and FGF-2, were originally isolated from brain and pituitary as mitogens for fibroblasts. However, FGF-1 and FGF-2, and fibroblast growth factors generally, are widely expressed in developing and adult tissues, and have multiple biological activities including angiogenesis, mitogenesis, cellular differentiation and repair of tissue injury (see e.g., Baird, A. et al., Cancer Cells 3:239-243 (1991) and Burgess, W. H. et al., Annu. Rev. Biochem. 58:575-606 (1989)).
According to the published literature, the FGF family now consists of at least twenty five members, FGF-1 to FGF-25. The 25 members of the FGF family range in molecular mass from 17 to 34 kDa and share 13-71% amino acid identity. Between vertebrate species, FGFs are highly conserved in both gene structure and amino-acid sequence.
The 25 members of the mammalian FGF family are differentially expressed in many tissues. The members are divided into subfamilies that have similar, though individually unique, patterns of expression. Some FGFs are expressed exclusively during embryonic development (for example, Fgf3, 4, 8, 15, 17 and 19), whereas others are expressed in embryonic and adult tissues. For example, FGF-16mRNA is predominantly expressed in the rat heart in adult tissues. However, in rat embryos, FGF-16mRNA is predominantly expressed in the brown adipose tissue (see e.g., Miyake A, et al. Biochem Biophys Res Commun 1998, 243:148-152).
Although most FGFs (FGFs 3-8, 10, 15, 17-19, and 21-25) have amino-terminal signal peptides and are readily secreted from cells, FGFs 9, 16 and 20 lack an obvious amino-terminal signal peptide but are nevertheless secreted (see e.g., Miyamoto M, et al. Mol Cell Biol 1993, 13:4251-4259). A third subset of FGFs (FGF 11-14) lack signal sequences and are thought to remain intracellular.
As noted above, the sub-family of FGF proteins comprising FGF-9, FGF-16, and FGF-20 lack a classical signal sequence, although they contain nuclear localization signals, and are secreted. These FGFs are expressed in the developing and adult nervous systems, suggesting a role in nervous system development and function (see e.g., Smallwood P. M., et al. Proc Natl Acad Sci USA (1996) 93:9850-9857). Indeed, a cDNA encoding FGF-20 was isolated from rat brain (see e.g., U.S. Pat. No. 6,797,695). Among FGF family members, FGF-20 is most similar to FGF-9 and FGF-16 (70 and 62% amino acid identity, respectively).
Numerous studies of human disorders as well as gene knock-out studies in mice indicate that FGFs are neurotrophic for cells of both the peripheral and central nervous system, and are important in the development of the skeletal system in mammals. A role in nervous system development and function is supported by in situ hybridization studies that show that FGF-20 mRNA is preferentially expressed in the substantia nigra pars compacta of the brain. Further support for a nervous system function is found in studies showing that in vitro, recombinant rat FGF-20 enhanced the survival of midbrain dopaminergic neurons in culture (see e.g., Ohmachi S. Biochem Biophys Res Commun 2000, 277:355-360).
In other studies, high levels of FGF-21 mRNA expression has been shown to occur in the liver, and human FGF-21 may play a role in the development of and recovery from liver disease. FGF-21 is also expressed in testis and thymus, and therefore may play a role in the development or recovery from disorders of testicular function or function of cells derived from the thymus (see e.g., U.S. Pat. No. 6,716,626).
Because of their wide ranging and potent activities, FGFs are pursued as therapeutic agents for a number of different indications, including wound healing, such as musculoskeletal conditions, bone fractures, ligament and tissue repair, tendonitis, bursitis, etc.; skin conditions, for example, burns, cuts, lacerations, bed sores, slow healing ulcers, etc.; tissue protection, repair, and the induction of angiogenesis during myocardial infarction and ischemia, inflammatory conditions and diseases (e.g., intestinal inflammation, including inflammatory bowel disease see e.g., Jeffers et al. Gastroenterology 2002; 123:1151-1162), in the treatment of neurological conditions such as neuro-degenerative diseases (e.g., Parkinson's disease), and stroke, in the treatment of eye disease, including macular degeneration, the pathology and treatment of cancer (see e.g., Jeffers, M., et al. Cancer Research 61, 3131-3138, April 1, (2001) and Jeffers et al. Expert Opinion on Therapeutic Targets (2002) 6(4):469-482) and for the treatment of diabetes. Unfortunately, the administration of therapeutic proteins such as FGF-9, FGF-18, FGF-20, and FGF-21 for the treatment of diseases and conditions can be complicated by, for example, short half life and mutagenic properties.
Poly(ethylene glycol) (“PEG”) is an exemplary polymer that has been conjugated to polypeptides. The use of PEG to derivatize peptide therapeutics has been demonstrated to reduce the immunogenicity of the peptides and improve pharmacodynamics including half-life. For example, U.S. Pat. No. 4,179,337 (Davis et al.) concerns non-immunogenic polypeptides, such as enzymes and peptide hormones coupled to polyethylene glycol (PEG) or polypropylene glycol. Between 10 and 100 moles of polymer are used per mole polypeptide and at least 15% of the physiological activity is maintained. In addition, the clearance time in circulation is prolonged due to the increased size of the PEG-conjugate of the polypeptides in question. The methods disclosed by Davis et al. are chemical PEGylation methods.
The chemical modification of peptides, frequently results in an undesirable loss of peptide activity, which is attributable to the non-selective nature of the chemistries utilized to modify the peptide. For example, when the modifying group is a water-soluble peptide, e.g., PEG, the principal mode of attachment of PEG, and its derivatives, to peptides is a non-specific bonding through a peptide amino acid residue. Studies of conjugates of water-soluble polymers and interleukin-2 (Fisher et al., Br. J. Haematol., 82: 654 (1992)), granulocyte colony stimulating factor (Satake-Ishikawa et al., Cell Struct. Funct., 17: 157 (1992)), tumor necrosis factor (Tsutsumi et al., Br. J. Cancer, 71: 963 (1996)) and Fibroblast Growth Factor (Clark, et al., J. Biol. Chem., 271:21969 (1996)) have revealed that chemical PEGylation of these proteins decreases the in vivo receptor binding activity of the peptides.
In many chemical PEGylation methods, poly(ethylene glycol) is added in an essentially random, non-specific manner to reactive residues on a peptide backbone. For the production of therapeutic peptides, it is clearly desirable to utilize a derivitization strategy that results in the formation of a specifically labeled, readily characterizable, essentially homogeneous product. A promising route to preparing specifically labeled peptides is through the use of enzymes, such as glycosyltransferases to append a modified sugar moiety onto a peptide.
Enzyme-based syntheses have the advantages of regioselectivity and stereoselectivity. Moreover, enzymatic syntheses are performed using unprotected substrates. Two principal classes of enzymes are used in the synthesis of carbohydrates, glycosyltransferases (e.g., sialyltransferases, oligosaccharyltransferases, N-acetylglucosaminyltransferases), and glycosidases. The glycosidases are further classified as exoglycosidases (e.g., β-mannosidase, β-glucosidase), and endoglycosidases (e.g., Endo-A, Endo-M). Each of these classes of enzymes has been successfully used synthetically to prepare carbohydrates. For a general review, see, Crout et al., Curr. Opin. Chem. Biol. 2: 98-111 (1998).
Glycosyltransferases modify the oligosaccharide structures on glycopeptides, producing specific products with good stereochemical and regiochemical control. Glycosyltransferases are used to prepare oligosaccharides and to modify terminal N- and O-linked carbohydrate structures, particularly on glycopeptides produced in mammalian cells. For example, the terminal oligosaccharides of glycopeptides have been completely sialylated and/or fucosylated to provide more consistent sugar structures, which improves glycopeptide pharmacodynamics and a variety of other biological properties. For example, β-1,4-galactosyltransferase was used to synthesize lactosamine, an illustration of the utility of glycosyltransferases in the synthesis of carbohydrates (see, e.g., Wong et al., J. Org. Chem. 47: 5416-5418 (1982)). Moreover, numerous synthetic procedures have made use of α-sialyltransferases to transfer sialic acid from cytidine-5′-monophospho-N-acetylneuraminic acid to the 3-OH or 6-OH of galactose (see, e.g., Kevin et al., Chem. Eur. J. 2: 1359-1362 (1996)). Fucosyltransferases are used in synthetic pathways to transfer a fucose unit from guanosine-5′-diphosphofucose to a specific hydroxyl of a saccharide acceptor. For example, Ichikawa prepared sialyl Lewis-X by a method that involves the fucosylation of sialylated lactosamine with a cloned fucosyltransferase (Ichikawa et al., J. Am. Chem. Soc. 114: 9283-9298 (1992)). For a discussion of recent advances in glycoconjugate synthesis for therapeutic use see, Koeller et al., Nature Biotechnology 18: 835-841 (2000). See also, U.S. Pat. Nos. 5,876,980; 6,030,815; 5,728,554; 5,922,577; and WO/9831826.
Glycosidases can also be used to prepare saccharides. Glycosidases normally catalyze the hydrolysis of a glycosidic bond. Under appropriate conditions, however, they can be used to form this linkage. Most glycosidases used for carbohydrate synthesis are exoglycosidases; the glycosyl transfer occurs at the non-reducing terminus of the substrate. The glycosidase takes up a glycosyl donor in a glycosyl-enzyme intermediate that is either intercepted by water to give the hydrolysis product, or by an acceptor, to give a new glycoside or oligosaccharide. An exemplary pathway using an exoglycosidase is the synthesis of the core trisaccharide of all N-linked glycopeptides, including the difficult β-mannoside linkage, which was formed by the action of β-mannosidase (Singh et al., Chem. Commun. 993-994 (1996)).
In another exemplary application of the use of a glycosidase to form a glycosidic linkage, a mutant glycosidase has been prepared in which the normal nucleophilic amino acid within the active site is changed to a non-nucleophilic amino acid. The mutant enzymes do not hydrolyze glycosidic linkages, but can still form them. The mutant glycosidases are used to prepare oligosaccharides using an α-glycosyl fluoride donor and a glycoside acceptor molecule (Withers et al., U.S. Pat. No. 5,716,812). Although the mutant glycosidases are useful for forming free oligosaccharides, it has yet to be demonstrated that such enzymes are capable of appending glycosyl donors onto glycosylated or non-glycosylated peptides, nor have these enzymes been used with unactivated glycosyl donors.
Although their use is less common than that of the exoglycosidases, endoglycosidases are also utilized to prepare carbohydrates. Methods based on the use of endoglycosidases have the advantage that an oligosaccharide, rather than a monosaccharide, is transferred. Oligosaccharide fragments have been added to substrates using endo-β-N-acetylglucosamines such as endo-F, endo-M (Wang et al., Tetrahedron Lett. 37: 1975-1978); and Haneda et al., Carbohydr. Res. 292: 61-70 (1996)).
In addition to their use in preparing carbohydrates, the enzymes discussed above are applied to the synthesis of glycopeptides as well. The synthesis of a homogenous glycoform of ribonuclease B has been published (Witte K. et al., J. Am. Chem. Soc. 119: 2114-2118 (1997)). The high mannose core of ribonuclease B was cleaved by treating the glycopeptide with endoglycosidase H. The cleavage occurred specifically between the two core GlcNAc residues. The tetrasaccharide sialyl Lewis X was then enzymatically rebuilt on the remaining GlcNAc anchor site on the now homogenous protein by the sequential use of β-1,4-galactosyltransferase, α-2,3-sialyltransferase and α-1,3-fucosyltransferase V. Each enzymatically catalyzed step proceeded in excellent yield.
Methods combining both chemical and enzymatic synthetic elements are also known. For example, Yamamoto and coworkers (Carbohydr. Res. 305: 415-422 (1998)) reported the chemoenzymatic synthesis of the glycopeptide, glycosylated Peptide T, using an endoglycosidase. The N-acetylglucosaminyl peptide was synthesized by purely chemical means. The peptide was subsequently enzymatically elaborated with the oligosaccharide of human transferrin glycopeptide. The saccharide portion was added to the peptide by treating it with an endo-β-N-acetylglucosaminidase. The resulting glycosylated peptide was highly stable and resistant to proteolysis when compared to the peptide T and N-acetylglucosaminyl peptide T.
The use of glycosyltransferases to modify peptide structure with reporter groups has been explored. For example, Brossmer et al. (U.S. Pat. No. 5,405,753) discloses the formation of a fluorescent-labeled cytidine monophosphate (“CMP”) derivative of sialic acid and the use of the fluorescent glycoside in an assay for sialyl transferase activity and for the fluorescent-labeling of cell surfaces, glycoproteins and gangliosides. Gross et al. (Analyt. Biochem. 186: 127 (1990)) describe a similar assay. Bean et al. (U.S. Pat. No. 5,432,059) discloses an assay for glycosylation deficiency disorders utilizing reglycosylation of a deficiently glycosylated protein. The deficient protein is reglycosylated with a fluorescent-labeled CMP glycoside. Each of the fluorescent sialic acid derivatives is substituted with the fluorescent moiety at either the 9-position or at the amine that is normally acetylated in sialic acid. The methods using the fluorescent sialic acid derivatives are assays for the presence of glycosyltransferases or for non-glycosylated or improperly glycosylated glycoproteins. The assays are conducted on small amounts of enzyme or glycoprotein in a sample of biological origin. The enzymatic derivatization of a glycosylated or non-glycosylated peptide on a preparative or industrial scale using a modified sialic acid was not disclosed or suggested in either of these references.
Enzymatic methods have also been used to activate glycosyl residues on a glycopeptide towards subsequent chemical elaboration. The glycosyl residues are typically activated using galactose oxidase, which converts a terminal galactose residue to the corresponding aldehyde. The aldehyde is subsequently coupled to an amine-containing modifying group. For example, Casares et al. (Nature Biotech. 19: 142 (2001)) have attached doxorubicin to the oxidized galactose residues of a recombinant MHCII-peptide chimera.
Glycosyl residues have also been modified to bear ketone groups. For example, Mahal and co-workers (Science 276: 1125 (1997)) have prepared N-levulinoyl mannosamine (“ManLev”), which has a ketone functionality at the position normally occupied by the acetyl group in the natural substrate. Cells were treated with the ManLev, thereby incorporating a ketone group onto the cell surface. See, also Saxon et al., Science 287: 2007 (2000); Hang et al., J. Am. Chem. Soc. 123: 1242 (2001); Yarema et al., J. Biol. Chem. 273: 31168 (1998); and Charter et al., Glycobiology 10: 1049 (2000).
Carbohydrates are attached to glycopeptides in several ways of which N-linked to asparagine and mucin-type O-linked to serine and threonine are the most relevant for recombinant glycoprotein therapeutics. A determining factor for initiation of glycosylation of a protein is the primary sequence context, although clearly other factors including protein region and conformation play roles. N-linked glycosylation occurs at the consensus sequence NXS/T, where X can be any amino acid but proline.
The present invention answers these needs by providing FGF mutants that contain newly introduced N-linked or O-linked glycosylation sites, providing flexibility in glycosylation and/or glycopegylation of these recombinant FGF mutants. Moreover, the invention provides an industrially practical method for the modification of N- or O-linked mutant FGF peptides with modifying groups such as water-soluble polymers, therapeutic moieties, biomolecules, and the like. Of particular interest are methods in which the modified mutant FGF has improved properties, which enhance its use as a therapeutic or diagnostic agent.